[Feature] Markers/tags for part of a scene

[Cummycummy]

Add the possibility to define a timestamp for a marker or tag, instead of only a starting time.

For example, we could be allowed to add a marker for a scene from 00:10 to 00:46.

This could then be used to create playlists of subscenes only marked with a specific marker or tag.

Example : randomly play all parts of scenes with marker/tag xyz

[Stashing-fr]

already "done"

#5311
#5633